1. Field of the Invention
This invention relates to methods and machines for producing continuous helical flighting for use in screw conveyors, augers and like material transporting, conveying or propelling means, and to machines incorporating such flighting.
Screw conveyors, augers and the like means incorporate or comprise a screw member for propelling particulate, granular or other free-flowing material (solid or liquid) along the length of the screw member in an axial direction as determined by the sense of rotation of the screw member. The propulsion of that material is achieved by the successive, often high speed turns of a continuous helical (spiral) blade (known in the art as flighting) which in most cases encircles, is secured on, and radiates from a central driving shaft which is arranged for rotation by an appropriate power source (manual or otherwise). However, some screw conveyors comprise solely such flighting, the flighting itself being driven by the power source, and the intrinsic strength of the flighting being sufficient to maintain the helical shape of the flighting whilst being driven.
In the case of a screw conveyor, the material being propelled by the successive turns of the blade is confined to the spaces between successive turns by a casing which encloses and cooperates with the outer periphery of the blade. In the case of hole-boring augers, however, the material being propelled by the successive turns of the blade is confined to the spaces between successive turns by the cylindrical wall of the hole being bored by the auger.
Though in some cases the screw member is of integral form, in most cases and for a variety of reasons, it is customary to form the helical blade separately, and independently of the driving shaft, first by rolling a metal strip between opposed mutually-inclined surfaces of a pair of rolls to form continuous rolled flighting, and then by securing it, for example by welding, on the driving shaft. The rolls may then be mounted in alignment with one another (i.e. with their respective rotational axes in a common plane), or in an offset manner (i.e. with their respective rotational axes in transversely spaced planes).
It is also customary (a) to use rolls of conical form, and (b) to form the helical blade from metal strip of rectangular cross section and uniform thickness (see, for example, patent specification U.S. Pat. No. 2,262,227 (FULSON)).
As a natural consequence of the rolling process to form a helical blade of which the length of an outer edge of the blade is substantially greater than that of an inner edge portion of the blade, the thickness of the blade at its outer edge, measured (for example) normal to the blade, is substantially less than that at said inner edge portion (see, for example, patent specification U.S. Pat. No. 2,262,227 (FULSON), FIGS. 12-16). In other words, in the rolling process, the uniform thickness, rectangular strip is converted Into a blade of which the thickness of the blade progressively reduces from said inner edge portion to the outer edge. That reduction in thickness typically amounts to 50% of the thickness of said inner edge portion of the blade. The thickness at said inner edge portion is normally substantially the same as (or even greater than) that of the metal strip from which the blade is rolled.
Patent specification U.S. Pat. No. 2,262,227 (FULSON) discloses one example of a process for rolling such a helical blade for use as flighting, using mutually-inclined conical rolls. Patent specification GB 736,838 (WURAG) discloses another process of rolling such an helical blade, using parallel conical rolls.
In some cases, the whole of the transverse width of the metal strip has been passed between such rolls (as in the above-mentioned prior patent specifications), so as to produce a helical blade in which the blade thickness varied across the whole of the radial extent of the blade, that is, from the inner edge of the blade to the outer edge thereof. In such cases, said inner edge portion has been constituted merely by that inner edge of the blade.
In other cases, only part of the transverse width of the metal strip has been passed between the rolls, so as to produce a helical blade in which the blade thickness varied in only that part of the metal strip that had passed between the rolls. In those cases, said inner edge portion has extended a substantial radial distance from said inner edge towards the outer edge of the blade.
Furthermore, it is found in practice that the wear of the blade due to the friction of the material being axially propelled by the blade is greatest at the outer periphery of the blade (i.e. at the fastest moving part of the blade), so that the part of the blade that is initially the thinnest is subjected to the greatest rate of wear (see, for example, patent specification U.S. Pat. No. 1,684,254 (BAILEY)). This causes the blade to be discarded or refurbished prematurely, at a time when the inner parts of the blade still have substantial thickness and life.
To overcome that disadvantage, patent specification U.S. Pat. No. 1,684,254 (BAILEY) provided at the outer edge of a cold rolled helical blade a “thickened reinforcement or bead”. Patent specification SU 772,664 (SAFRONOV) also provided a thickened outer edge portion on a rolled helical blade. Patent specification GB 472,254 (BARKER) disclosed the use of a thickened outer edge portion on a cast form of Archimedean screw, to overcome the greater wear that occurs at that portion of the screw.
Patent specification SU 772,664 (SAFRONOV) also discloses a rolling process in which (a) the main rolls 1,2 for producing the helical blade from a strip of rectangular transverse cross section have stepped rolling surfaces, (b) the cone angles of the main rolls 1,2 is relatively small, (c) the angle of inclination of their rotational axes is likewise relatively small, (d) an auxiliary pair of edge-forming rolls 6,7 is used to simultaneously thicken up the outer edge portion of the helical blade, and (e) the use of an edge-forming rolling pressure directed transversely to the main helix-forming rolling pressure is essential to the process described. In addition, the main rolls 1,2 and the auxiliary rolls 6,7 are capable of rolling only one size of strip material 8 and of producing only one size of helical blade 9.
In U.S. Pat. No. 5,678,440 issued Oct. 21, 1997 to Hamilton, which is incorporated herein by reference, shows a continuous screw conveyor or auger, the rotatable screw member (12) comprises a helical radial blade (28) (known as “flighting”) which is preferably carried on a central driving shaft (26). The flighting (28) was formed by rolling a rectangular metal strip of uniform thickness between a pair of opposed, preferably offset, conical rolls (56, 58) in contrast to prior art rolls which had similar unstepped conical rolling surfaces, and produced a helical blade of which the radial thickness reduce progressively from the inner helical edge (30) of the blade to the outer helical edge (32). The Hamilton device provided on at least one of the rolls (58) a stepped conical rolling surface (94) formed so as to exert less rolling pressure on an outer portion of the helical blade (28) being formed, thereby to produce a blade in which the outer portion is of a thickness (preferably uniform) which was no less than and preferably greater than that of an inner part of the blade lying immediately radially inwards thereof.
U.S. Pat. No. 8,069,973 B2 issued 6 Dec. 2011 to Winnobel et. al., shows a method whereby a portion of the carrying surface of the helical blade between the inner and outer edges (See FIG. 11) is formed to produce a concave section 24. FIG. 7 shows a conical roll where the conical angle of the stepped portion 68 is the same as the overall conical angle of the roll and parallel with the conical angle of the base section 64. This prevents any progressive increase in thickness in the outer portion of the flighting 26. Further, any deflection of the rolls caused by introduction of the metal strip between them will reduce thickness in the outer portion 26 with negative impact upon the wear resistance of this portion of the flighting.